First of all, wrong forum, this is for the Community forum BETA, which is what you made this post on.
Second: They are inviting solely on experience for multiple reasons. They don't want people to play just so they can access content that is not released yet. They also invite people based on what they usually play (tank support, jungle, ect.) because that might be something they need to test currently.
Being a BETA tester is a privilege, not a right, and SHOULD be used as a way for the community to assist in fixing bugs before they go live. That is a problem of a lot of game BETAs released by other developers, they are really just demos to put their game in the public to get sales on release.
And before you get mad at me, I'm not a BETA tester currently either, I just know how the system works and am waiting patiently ;) 